The catheter-tip velocity transducer with proximal pressure port and distal stabilizing tip has been utilized to study blood velocity, acceleration, pulsatile power and vascular impedance in the pulmonary and systemic circulation in man. These measurements have allowed us to evaluate the effects of cardioactive pharmacologic agents and stress on the cardiovascular system on a beat-to-beat basis. Patients with all forms of heart disease have been studied and several interesting observations have been made. These include the following: (1) quantitation of aortic incompetence, (2) the detection and quantitation of pulmonary blood flow in patients with left-to-right shunt, (3) the detection of the change of the direction of pulmonary artery blood flow in a patient with patent ductus arteriosus, and (4) the quantitation of a decrease in pulmonary artery pressure and increase in pulmonary artery blood flow in a patient with primary pulmonary hypertension treated with intravenous Tololazine and intravenous Isuprel, (5) the measurement of right and left ventricular pulsatile power, velocity and acceleration in patients with normal ventricular performance and during myocardial ischemia induced by stress.